Weil-Mclain Boiler Mystery Leaking

[DYIDangerous]

I have a Weil Mclain WGO-5 boiler. ITT Bell Gossett HFT-60 diaphragm expansion tank next to the boiler. When the boiler is off the pressure gauge says 3 PSI and temperature around 167 degrees. During a long burn the pressure rises to 25-28psi and the temperature hits 175 area. No water leaks from the pressure release valve during the burn. When the system shuts off some water comes out via the PRV. I am emptying a 5 gallon bucket every 5 days. In November 2018 burner technician replaced PRV and problem abated briefly. Expansion tank taps "hollow" on the bottom 1/3 when system off.

Any ideas?

 

[maple1]

What is your system volume?

Sounds to me like your expansion tank could be toast, hole in bladder. If water comes out of the air fitting when you check it, that would confirm. Could also be your expansion tank has way too much air precharge in it but if this is an issue that developed over time or recently that shouldnt be it.

 

[NateB]

I would agree with Maple1 for the pressure to rise 22 to 25 psi in just 8 degree rise in temp, there must not be much room for expansion. The other thing that seems odd is the pressure is only at 3 psi when the boiler is at 167F? Maybe the pressure gauge is screwed up and the system is starting at a much higher PSI, and you are pushing it over the PRV limit. Do you have an automatic fill, or manual?

 

[peakbagger]

Does sound like a expansion tank. FYI, those automatic fill valves on boilers have a diaphragm that will get brittle and do strange things with water pressure. I think they can be rebuilt but most folks just put in new one.

 

[maple1]

Does sound like a expansion tank. FYI, those automatic fill valves on boilers have a diaphragm that will get brittle and do strange things with water pressure. I think they can be rebuilt but most folks just put in new one.

Yes they certainly can. I was assuming the pressures mentioned were accurate. But there might be a wonky gauge also as Nate mentioned - which would almost have to be the case if there is a fresh fill setup hooked up and it only reads 3psi. (Actually, mine won't read that low, they bottom out around 5 I think). Gauges can certainly go wonky. And if the gauge is wonky, it could all be in the fresh fill setup and the tank might be OK.

Sometimes we just have to be there...

 

[DYIDangerous]

Arrggghhh. I am skilled enough to replace an expansion tank (I think) but replacing gauges and auto fill valves seems perhaps a bridge too far. I want to sell my house - this is the only mechanical issue. Don't want to drop a bunch of money on furnace guy....

 

[NateB]

https://www.supplyhouse.com/Zurn-HG...7PaQG6BqL9e8FxqlYkvHrsw9k4YtnPcgaApH7EALw_wcB

This gauge would be a quick way to check the pressure if you have a drain/fill on your boiler. Once you get a reading you have confidence in, I would turn off the auto fill, and get the pressure to around 12 psi, and run the boiler again. If it is the auto fill valve, it is not too hard to replace. Get a replacement from supply house and pay a plumber to swap it, if you don't want to do it yourself.

 

[maple1]

Might not be that hard a fix, depending how your system was plumbed to start with. Lots of isolation valves would come in handy. Hopefully you have some.

Good suggestion above on the pressure gauge. First thing you'd want to know is pressures, accurately. If there is a problem with the fresh fill unit, it might not need replacing, it might just need taken apart & cleaned up. They can get dirty inside. Another free easy diagnosis is check to see if water comes out of your expansion tank when you check the air pressure at the air pressure fitting. If it does, you definitely know the bladder has a hole in it.

EDIT: on the gauge thing, look around all your piping to see if there is a plug anywhere at all. You could maybe put a new one where a plug is rather than taking the old one out. Or look for a place you could T one in easily. Any shut off or other drain valves with an open end you could just screw something into? Never know, all kinds of different things on different systems.

 

[DYIDangerous]

Might not be that hard a fix, depending how your system was plumbed to start with. Lots of isolation valves would come in handy. Hopefully you have some.

Good suggestion above on the pressure gauge. First thing you'd want to know is pressures, accurately. If there is a problem with the fresh fill unit, it might not need replacing, it might just need taken apart & cleaned up. They can get dirty inside. Another free easy diagnosis is check to see if water comes out of your expansion tank when you check the air pressure at the air pressure fitting. If it does, you definitely know the bladder has a hole in it.

EDIT: on the gauge thing, look around all your piping to see if there is a plug anywhere at all. You could maybe put a new one where a plug is rather than taking the old one out. Or look for a place you could T one in easily. Any shut off or other drain valves with an open end you could just screw something into? Never know, all kinds of different things on different systems.

 

[DYIDangerous]

Interestingly I connected a bicycle pump to the valve at the bottom of the expansion tank. No water leaked from the valve. It read less than 5 PSI. I pumped up the expansion tank to 10-12PSI (12 is recommended on the tank). The rate of water coming from the pressure release valve has slowed by 50-75%. Thoughts on what this means?

 

[maple1]

You can make more trouble playing with an expansion tank, if you aren't careful.

It sounds like yours lost its air. For some reason. The main question is where did it go? By putting air back in, you gained expansion room. But what is your boiler/system pressure now? There needs to be a balance.

The proper way to set up a bladder expansion tank, and the system to go with it, if I can type it quickly without getting it wrong, is first to isolate it from the rest of the system. That means valving it off, maybe unhooking it. Then you would drain the water all out from it. That might require disconnection if your piping isn't valved & plumbed to allow it. Once it has no water in it, and the connection hole is open to the air, you would fill the air side to specd pressure. 12 is common. At the same time, you would get your boiler pressure right by either adding or draining water. Make it the same as the expansion tank. Do it with a cold boiler. (With it at the coldest temps it would see in a normal cycle of operating). Once you have the boiler and the air side of the expansion tank at same water & air pressure, you hook the expansion tank back up, then open it to the system.

With what you did, shortcuts may be possible. But when you added the air, you would also need to watch the water pressure on the boiler. And keep it the same as the air pressure. Either by adding or draining water. If you added air and the boiler pressure was a few pounds more than the air pressure, the tank would be full of or almost full of water and it would have no expansion capacity. That might be why you are still leaking.

EDIT: Also, if you don't use a low pressure air guage, your air pressure readings might not be accurate.